1. Field of the Invention
The present invention relates to an interface system for use in a printer system such as a laser beam printer for recording information transferred from a host computer or the like on a recording medium such as a recording sheet, and more particularly to an interface system for use in a so-called page printer capable of printing, e.g., one page information at a time with help of a recording device having a predetermined storage capacity commonly referred to as a bit map memory with a facilitated editing feature. Incidentally, in the present specification, in addition to the above-described page printer capable of printing one page of information at a time, other types of printers adapted for printing a half page or a plurality of pages of information at a time will be generically referred to as the page printer.
2. Related Arts of the Invention INVENTION
The recording information provided by the host computer to the page printer is generally transferred as serial data via a single signal line. If the recording information comprises character codes representing character information to be recorded, font data in the form of a bit map for each character code is retreaved from a font memory to be written into a determination storage area on the bit map memory and this data retreaval-write operation is repeated. On the other hand, if the recording information comprises graphic image data representing graphic image information directly corresponding to a bit map to be recorded, raster image data transmitted as serial data in correspondance to the graphic image data is successively written from a starting storage area of the bit map memory.
Incidentally, as a printer for recording information such as character information or graphic image information on a recording medium, an impact type wire-dot printer is widely used. This wire-dot impact printer has a recording head including a plurality of vertically aligned wire pins. In operation, as this recording head is moved laterally, the wire pins selected in accordance with the recording information strike an ink ribbon against a recording medium thereby printing an image thereon. Accordingly, when this wire-dot impact printer as an output terminal device receives from a host computer recording information directly corresponding to a bit map to be recorded, the recording information is transferred as serial data consisting of a plurality of bits corresponding to the number of the wire pins re-arranged in the lateral alignment.
That is to say, a conventional recording system must include a specific combination of host computer and a printer as an output terminal device therefor because of the difference in the protocol of the recording information communicated therebetween.
However, the page printer represented by the increasingly popular laser printer has the advantages of high speed and high resolution image recording and also of low noise generation. Then, there has been a demand for using the laser beam printer in place of the wire-dot printer in a conventional recording system by sharing the same host computer in order to achieve high recording efficiency and high quality recording image.
Then, in order to use the page printer such as the laser printer in the conventional recording system, because of the aforementioned difference between the protocols of the recording information provided from the host computer to the impact printer and to the page printer, it becomes necessary to convert the recording information adapted for the wire-dot printer into serial data suited for the page printer.
One conceivable means to overcome the above problem is to provide a hardware interface. In this case, even if the system is to be adapted for a single protocol, the addition of the hardware will bring about a cost increase. Further, if the system is to be adapted for a plurality of different protocols, this will make the system significantly complicated and costly. Accordingly, in order for the system to commonly use the page printer without incurring cost increase and with adaptability for many different types of protocols, it becomes necessary to provide a protocol-converting emulation software which enables the system to process data under various protocols only through minor changes in the data processing.
Moreover, as described hereinbefore, the page printer such as the laser beam printer generally has a higher recording resolution than the wire-dot impact printer. Accordingly, if this page printer is used in place of the wire-dot impact printer only by dot-by-dot corresponding the data for the wire-dot impact printer, the page printer will provide the recording information only in a physically reduced scale.
For the above reason, even with the protocol-converting emulation software, if there exists the problem of resolution difference as described above, an additional processing becomes necessary for enlarging the protocol-converted data. Such additional processing necessitates an undesirable delay in the recording speed of the system.